1. Field of the Invention
In one of its aspects, the present invention relates to an ultraviolet radiation light emitting diode (LED) device. In another of its aspects, the present invention relates to a fluid treatment system comprising an ultraviolet radiation LED device.
2. Description of the Prior Art
Fluid treatment systems are known generally in the art.
For example, U.S. Pat. Nos. 4,482,809, 4,872,980, 5,006,244, 5,418,370, 5,539,210 and Re:36,896 (all in the name of Maarschalkerweerd and all assigned to the assignee of the present invention) all describe gravity fed fluid treatment systems which employ ultraviolet (UV) radiation.
Generally, such prior fluid treatment systems employ an ultraviolet radiation lamp to emit radiation of a particular wavelength or range of wavelengths (usually between 185 and 400 μm) to effect bacterial kill or other treatment of the fluid being treated. Conventional ultraviolet radiation lamps are so-called “low pressure” mercury lamps and “medium pressure” lamps.
The art in low pressure mercury lamps has evolved with the development of the so-called Low Pressure, High Output (LPHO) and amalgam UV radiation lamps. These lamps have found widespread use in UV radiation water treatment systems, particularly those used for treatment of municipal drinking water and wastewater. As used herein, the term “low pressure” UV radiation lamp is intended to encompass conventional UV radiation lamps, LPHO UV radiation lamps and amalgam UV radiation lamps.
In recent years, an interest has evolved in light emitting diodes (LEDs) as an alternate source of ultraviolet radiation.
With respect to UV LEDs, the prior art approaches have revolved around grouping individual LEDs into lighting systems that would be used as a light source.
For example, International Publication Number WO05/031881 [Jensen] teaches a tubular LED light source that involves substitution of a cylindrical group of LEDs for a standard cylindrical lamp in a lamp sleeve in conventional fluorescent lighting.
A similar design for the UV LED light source in a portable water disinfection system is taught by International Publication Number WO04/028290 [Maiden].
United States Patent Application Publication US2005/0000913 [Betterly] teaches a fluid treatment system in which this scheme is inverted—i.e., a scheme wherein an outside cylinder of LEDs directs UV light inwards toward a transparent pipe where the water to be disinfected flows.
The disadvantage of the approaches taught by Jensen, Maiden and Betterly is the difficulty in achieving heat extraction from the individual LEDs arranged in their respective geometries. A further disadvantage of the approaches taught by Jensen, Maiden and Betterly is the low UV power densities possible with individual light sources. The low power density possible in a practical disinfection device such as that of Maiden results in low possible flow rates for disinfecting water. That is why this system is a small personal use system. An alternate reactor geometry of Betterly has a rectangular array of LEDs that are shown protruding from a rectangular weir (see FIG. 4 of Betterly)—this makes cleaning very difficult once fouling occurs in the disinfection reactor. FIG. 4 of Betterly is based on a standard epoxy encapsulant that would surround the LED chip giving the illustrated bullet-shaped profile. Epoxy encapsulation for a UV LED is not feasible due to the fact that a conventional epoxy encapsulant is susceptible to degradation over time upon prolonged exposure to UV radiation.
International Publication Number WO 05/31881 [Scholl] teaches a disinfecting lamp using semiconductors with AlGaN alloys. No practical demonstration of these lamps is presented. Scholl teaches that the current effectiveness of AlGaN LEDs “can be improved from the current 20% to 40%”. Scholl further teaches that the power density of a hypothetical LED of 1 W UV power output and 40% effectiveness with a 1 mm2 area is 40 W/cm2. This would compare favorably to standard mercury lamps with power densities of 0.04-1.5 W/cm2. However, there are two problems with this statement. First, the power density would only be 40 W/cm2 directly above the LED chip. Over the entire area of the device of a sample area of 1 cm2, the power density would drop to an average of 0.4 W/cm2. Second, the state of the art UV for output in UV LEDs emitting in the germicidal wavelength region of ˜240-280 run is only ˜1 mW at 280 nm (see J. P. Zhang et al., “AlGaN-based 280 nm light-emitting diodes with continuous-wave power exceeding 1 mW at 25 mA”, Applied Physics Letters 85, p. 5532-5534, 2004).
Thus, the state of the art average power density for a UV LED is therefore ˜1 mW/cm2, which is much less than that of mercury lamps. In Zhang et al, the efficiency of the state of the art 280 nm LED is only 0.85% versus the 20-40% mentioned above.
Thus, despite the purported advances made in the art, there is an ongoing need for an actual UV LED that can be used as an efficient and effective disinfection light source.